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IDENTIFIKASI SIFAT OPTIKMINERAL
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MIKROSKOP POLARISASI
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Tahap Identifikasi
ortoskop nikol sejajar: warna,
pleokroisme, belahan,pecahan, relief,
indeks bias, ukuran mineral
ortoskop nikol silang: warna
interferensi, Bf, orientasi optik, sudut
pemadaman, kembaran.
konoskop: sumbu optik, tanda optik,
sudut 2V
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NIKOL SEJAJAR
Warna
pleokroisme,
belahan, pecahan,
relief,
indeks bias
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Ortoskop Nikol Sejajar
Warna merupakan pencerminan dari
kenampakan daya serap atau absorpsi
panjang gelombang dari cahaya yang
masuk pada mineral anisotropic.
Idiochromaticadalah warna asli mineral
Allochromaticadalah warna akibat adanya
pigmen lain seperti inklusi kristal-kristal
halus atau adanya elektron-elektron dari
logam-logam transisi (Cr, Fe, Mn, dll).
1. Warna
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Idiokromatik
allokromatik
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Gejala perubahan warna mineral pada
ortoskop tanpa nikol atau nikol sejajar bila
meja objek diputar hingga 90, disebut
dengan pleokroisme.
2. Pleokroisme
Jenis-jenis pleokroisme mineral dapat dibagi kedalam 2
(dua) golongan, yaitu :
Dwikroik (dichroic), bila terjadi perubahan dua warna
yang berbeda, contoh pada mineral bersistem kristalhexagonal dan tetragonal.
Trikroik (trichroic), bila terjadi perubahan tiga warna yang
berbeda. Terjadi pada mineral dengan sistem kristal
ortorombik, monoklin dan triklin.
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Bentuk-bentuk mineral dapat dibagi kedalam
tiga bagian, yaitu :
Euhedral, bila kristal dibatasi oleh bidangkristalnya sendiri.
Subhedral, bila kristal dibatasi hanya sebagian
bidang kristalnya sendiri.
Anhedral, bila kristal sama sekali tidak dibatasi
oleh bidang-bidang kristalnya sendiri.
Bentuk Mineral
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Klorit anhedral
Olivin euhedral
Plagioklas subhedral
Kuarsa
hexagonal
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Belahan (Cleavage)
Setiap mineral mempunyai kemampuan dan
kecenderungan untuk terpisah menjadi bagian yang lebih
kecil. Apabila bidang-bidang tersebut berbentuk lurus
dengan arah tertentu sesuai dengan bentuk kristalnya,
bidang tersebut adalah belahan (cleavage).
Apabila bidang-bidang tersebut tidak dikontrol olehbentuk kristalnya (struktur atom), tetapi dikontrol
oleh faktor lain seperti kembaran, maka bidang
tersebut dinamakanparting.
Jika bidang-bidang kecil dari mineral tidak lurus
dengan arah yang tidak teratur dan tidak dikontrol
oleh struktur atomnya, maka bidang tersebut
adalah pecahan (fracture).
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Indeks bias
Indeks bias merupakan fungsi dari perjalanan
sinar di dalam medium yang berbeda.
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Relief suatu kenampakan yangtimbul akibat adanya
perbedaan indeks biasmineral dengan media
yang ada di sekitarnya.
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Indeks Bias
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Plagioclase and Augite in a Diabase
The photos show mostly labradorite (a variety of plagioclase) with several grains of augite(a variety of
clinopyroxene). The labradorite is clear and the augitehas a typical dusty geen-gray color in PP light. Theplagioclase exhibits well developed albite twins, giving a zebra-striped appearance in XP light. Plagioclase,
especially plagioclase in igneous rocks, has a tendency to alter to micas and clays over time. This sample is
fairly fresh, but some plagioclase grains are slightly altered -- the alteration is visible as a sort of fine grained
grunge on grains near the top center of the photo. Note that the augite has significantly higher reliefthan the
labradorite.
http://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/plagioclase.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/cpx.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/cpx.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/cpx.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/twinning.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/relief.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/relief.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/twinning.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/cpx.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/cpx.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/cpx.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/plagioclase.htm -
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Plagioclase, Hornblende, Quartz and Biotite in a Gneiss
The clear minerals (PP) in this thin section are plagioclase (twinned) and quartz(not twinned). The green mineral (PP) is
hornblendeand the brown mineral is biotite(PP). The biotite is pleochroic, and some grains have a color similar to that
of the hornblende. The two can be tough to distinguish, but biotite has a more flakey (micaceous) habit.
Note the complex twinningin the plagioclase; there are two sets of twinsnearly perpendicular in the largest grain. In
other grains the twinningis discontinuous.
http://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/twinning.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/quartz.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/biotite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/pleoch.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/twinning.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/twinning.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/twinning.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/twinning.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/twinning.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/twinning.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/pleoch.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/biotite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/quartz.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/twinning.htm -
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Microcline with Quartz, Hornblende and Biotite
These photos show several grains of microcline (K-feldspar) with well developed cross-hatched twinning(XP).Quartzand plagioclaseare also present; they have color and interference colorssimilar to microcline's but lack
microcline twinning. Brown biotiteand green hornblendecan be seen in the PP view. One hornblendegrain
has a diamond shape and shows hornblende's characteristic two cleavagesat angles of 60oand 120o. A few
grains of magnetite are in the lower right.
http://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/twinning.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/quartz.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/plagioclase.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/twinning.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/biotite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/cleavage.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/cleavage.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/biotite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/twinning.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/plagioclase.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/quartz.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/twinning.htm -
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Epidote in a Highly Altered Basalt
The photos show epidote that has filled an amygdule in a highly altered basalt. The colorof the epidote is
typical: a sort of off-color yellow-green. The interference colors, too, are classic: various shades of pastels
within individual grains. The opaque material around the amygdule is a mixture of glass, hematite and chlorite.
Note several bubblesintroduced when the thin section was made.
http://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/pleoch.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/bubbles.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/bubbles.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/pleoch.htm -
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Epidote and Hornblende in a Mafic Schist
The photos show pleochroichornblende(green hues; PP) and epidote (clear; PP) in a mafic schist. Note the
epidote grains show multiple interference colorscreating zones or concentric rings in most grains (XP). Alsonote that some of the hornblendeshows a hint of a diamond shape and of amphibole's characteristic 60o-120o
cleavage angle.
http://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/pleoch.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/cleavage.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/cleavage.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/pleoch.htm -
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Chlorite, Glaucophane and Epidote in a Blueschist
Green chlorite, blue glaucophane(an amphibole), clear white micaflakes (bottom center and right) and a
number of small high-reliefepidote grains (most are wedge-shaped) are visible in PP light. In XP light thechloriteshows anomalous interference colors, the glaucophane shows 2nd order interference colors, in places
somewhat masked by the blue colorof the mineral. The mica flakes show obvious mottled 2nd order
interference colors.The epidote grains are hard to pick out in XP light
http://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/naamph.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/muscovite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/relief.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/pleoch.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/pleoch.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/relief.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/relief.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/relief.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/muscovite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/naamph.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htm -
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Titanite (sphene) in a Quartz Monzonite
This view shows a titanite "wedge" surrounded by magnetite, quartzand feldspar, and minor epidoteand chlorite. The
titanite has very high reliefand its interference colorsare of such high order that they are hard to identify. The "wedge"
or diamond shape of this grain is typical for titanite when it is euhedral (in many rocks it is not). Just above and to the
right of the titanite is a compound grain composed of epidote(high order blue-orange-red interference colors) and
chlorite(green in PP, nearly extinct in XP). Also present are three grains of magnetite (opaque
http://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/quartz.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/epidote.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/relief.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/epidote.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/epidote.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/relief.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/epidote.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/quartz.htm -
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These photos show a large euhedral garnet in a sea of mostly omphacite(a high pressure sodic pyroxene),
titanite, and a few flakes of white mica. The garnetis slightly altered to chloritealong its edges; note the
anomalous interference colorsin the XP view. The omphaciteis pale green (PP) with interference colorsthat
range up to first order red (XP). In a few places, where higher-order colorscan be seen, the omphaciteis being
replaced by hornblende. The titanite crystals are small, have very high relief(PP), and appear as irregular
elongate grains, some of which have acute terminations. Several flakes of white micaare present -- they are the
clearest grains visible in the PP view.
Garnet and Titan ite in an Eclogite
http://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/garnet.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/napyrox.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/napyrox.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/muscovite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/garnet.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/napyrox.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/napyrox.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/relief.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/muscovite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/muscovite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/relief.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/napyrox.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/napyrox.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/garnet.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/muscovite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/napyrox.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/napyrox.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/napyrox.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/napyrox.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/garnet.htm -
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RutileThe views above show several large grains of brownish rutile (PP). The rutile is surrounded by mostly quartz(on
the left and bottom of the photo) and several flakes of clear micaon the right. Rutile has very highbirefringence. Just a hint of high order pastel interference colorscan be seen here (XP).
Although not distinctive in these photos, kyaniteis present just above the two large rutile grains, and also to
the left of the smaller grain near the center of the field of view. The kyanite has slightly higher reliefthan
surrounding minerals, but otherwise is hard to pick out. It is clear (PP) and shows first order gray interference
colors(XP).
http://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/quartz.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/muscovite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/kyanite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/relief.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/relief.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/kyanite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/muscovite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/quartz.htm -
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The PP view shows biotitein various shades of brown, clear quartz, and light yellow brown twinnedrutile.The
rutile is rimmed by an opaque mineral, probably magnetite. Minor sillimaniteis present as one high-reliefmassnear the right side, just below center. One grain of clear plagioclaseis just above the largest rutile. In the XP
view, the large black grain is quartzthat happens to be near extinction. Biotiteshows typical second order
interference colors. The rutile shows no distinct interference colorsbecause the color of the grain masks the
interference colors.
B iot i te-Si ll iman ite Sch ist
http://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/biotite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/quartz.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/twinning.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/sillimanite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/relief.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/plagioclase.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/quartz.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/biotite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/biotite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/quartz.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/plagioclase.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/relief.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/relief.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/relief.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/sillimanite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/twinning.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/quartz.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/biotite.htm -
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Epidote-Clinozoisite
The diamond-shaped original crystal was hornblendebut it has been replaced byother minerals. In PP light, chloriteand epidote both appear light green (but thechloritehas a more "micaceous" character). Under crossed polars (XP) they aredistinguished because the chlorite shows anomalous green-gray interference colorswhile the epidote shows upper second order interference colors. Th opaque mineral is
magnetite; quartzand feldsparsurround the amphibole grain.
http://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/quartz.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/plagioclase.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/plagioclase.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/quartz.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htm -
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Jawab pertanyaan1. Tuliskan tujuan mempelajari Mineral Optik dan hubungannya dengan
mata kuliah yang telah saudara pelajari.
2. Mengapa dalam menganalisis sifat optik menggunakan mikroskopkhusus yaitu mikroskop polarisasi?
3. Jelaskan hubungan bagian-bagian mikroskop dengan sifat optik yangakan ditentukan.
4. Jelaskan cara penentuan batuan atau mineral yang akan dianalisis sifatoptiknya.
5. Jelaskan sifat cahaya jika mengenai medium kristalin, lengkapi dengangambar.
6. Jelaskan terjadinya addisi dan substraksi cahaya pada medium kristalin
7. Jelaskan perbedaan medium isotrop & anisotrop, disertai dengan contohmineral
8. Gambar dan jelaskan pembiasan cahaya jika melewati medium isotrop &anisotrop.
9. Jelaskan perbedaan sumbu-sumbu optik pada mineral uniaxial danbiaxial.
Kumpul besok, selasa 13 Maret 2012 jam 10.00 di Lab. Petrografi.
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Nikol Silang
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Nikol Silang
Identifikasi mineral secara optik dengan
ortoskop nikol silang, menggunakan
lensa polarisator dan analisator. Dengan
ketentuan bahwa arah getar polarisator
harus tegak lurus terhadap arah getar
analisator.
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Sifat-sifat optik yang diamati
adalah :
Warna interferensi,
Birefringence(bias rangkap),Orientasi optik,
Sudut pemadaman dan jenis
pemadamanKembaran
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Warna Interferensi
Warna interferensi adalah warna yangdihasilkan dari cahaya yang diteruskan melaluianalisator kepada mata pengamat. Warna
interferensi terjadi pada mineral anisotropkarena adanya selisih harga indeks bias sinarordiner dan sinar ekstraordiner. Rangkaianwarna interferensi terbagi menjadi beberapa
orde, mulai dari orde pertama hingga ordekeempat.
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Bias Rangkap (Birefringence)
Cahaya yang masuk dalam media anisotrop
akan dibiaskan menjadi 2 (dua) sinar, yang
bergetar dalam 2 (dua) bidang yang saling
tegak lurus. Harga bias rangkap merupakanselisih maksimum kedua indeks bias sinar yang
bergetar dalam suatu mineral.
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Epidote-Clinozoisite
The diamond-shaped original crystal was hornblendebut it has been replaced byother minerals. In PP light, chloriteand epidote both appear light green (but thechloritehas a more "micaceous" character). Under crossed polars (XP) they aredistinguished because the chlorite shows anomalous green-gray interference colorswhile the epidote shows upper second order interference colors. Th opaque mineral is
magnetite; quartzand feldsparsurround the amphibole grain.
http://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/quartz.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/plagioclase.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/plagioclase.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/quartz.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htm -
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Pada mineral yang mempunyai
sistem kristal tetragonal, hexagonal
dan trigonal, selisih indeks bias
maksimum terdapat pada sayatan
yang sejajar sumbuc kristalografi,
karena pada sayatan ini sinar yang
bergetar adalah sinar biasa
(ordiner) dan sinar luarbiasa
(extraordiner) yang sesungguhnya.
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Perjalanan Sinar pada Ortoskop
Nikol Silang yang Menghasilkan
Birefringence.
Pada medium anisotrop, cahaya
dari lampu akan terpolarisasi danketika masuk pada media
kristalin, cahaya tersebut
diuraikan menjadi 2 (dua)
cahaya yang saling tegak lurus.
Bidang getar kedua sinartersebut adalah OA dan OB
pada bidang elips yang tegak
lurus terhadap arah sinar.
Kedua sinar tersebut masuk ke
dalam analisator dandikumpulkan menjadi menjadi
satu getaran dalam bidang CD.
Kedua getaran tersebut akan
mengalami interferensi (Fresnel
& Arago).
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Orientasi optik
hubungan antara sumbu panjang kristalografimineral dengan sumbu indikatriknya (arahgetaran sinar). Pada umumnya sumbu
terpanjang kristalografi adalah sumbu-ckristalografi.
Tetapi pada kelompok filosilikat, umumnyasumbu-c kristalografi merupakan sumbu
terpendek, sedangkan yang terpanjang adalahsumbu-a kristalografi.
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Orientasi Optik a)
sumbu-c sejajardengan polarisator,
b) putar meja optic
45, c) Jika sumbu-
c sejajar dengansumbu indikatrik
sinar Z maka
orientasi optiknya
length-slow
(Nesse, 1986).
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Sudut Gelapan dan jenis Gelapan
(Extinction)
Gelapan atau pemadaman adalah keadaan
mineral pada kedudukan warna interferensi
minimum, terjadi apabila sumbu indikatriks
(arah getar sinar) mineral sejajar dengan arahgetar analisator atau polarisator.
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Jenis Gelapan
Gelapan sejajar (paralel), terjadi bila pemadamanberada pada posisi dimana sumbu panjangataupun belahan mineralnya sejajar sumbu-c dansejajar pula dengan benang silang (c ^ X,Z = 0atau c ^ X,Z = 90. Gelapan ini umumnya terjadipada sistem kristal tetragonal, heksagonal,trigonal,dan ortorombik.
Gelapan simetris, terjadi bila pemadaman padaposisi simetris (c ^ X, Z = 45). Umumnya pada
sayatan mineral system orthorombik, monoklin,misalnya pada jenis mineral piroksin danamphibol.
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Jenis Gelapan
Gelapan miring, gelapan jenis ini merupakanpemadaman yang terjadi pada posisi dimana
sumbu panjang kristal (belahan yang sejajar
sumbu-c) membentuk sudut dengan arah getar
analisator dan polarisator (c ^ X,Z = 1 - 44).
Gelapan bergelombang, gelapan jenis ini terjadi
karena keseluruhan mineral telah mengalami
tekanan namun belum sampai rekristalisasi
secara sempurna, umumnya pada pada kuarsa.
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Jenis-Jenis
Pemadamana) Paralel,
b) Miring
c) Simetri
d) Tidak
Mempunyai
Pemadaman
(Nesse, 1986)
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Kembaran
kembaran nampak sebagai lembar-lembar yang
memperlihatkan warna interferensi dan
pemadaman yang berbeda.
terjadi gangguan pada waktu proses kristalisasiyang menyebabkan kembaran tumbuh. Dapat juga
terjadi karena adanya proses deformasi pada waktu
kristal tersebut sudah terbentuk (kembaran
deformasi).
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Kembaran
Pada kembaran tumbuh, lembar-lembar
kembarannya tertentu dan bidang batasnya
lurus.
kembaran deformasi, lebar lembar
kembarannya berubah dan batasnya sering
melengkung.
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tugas
Diskripsi sifat optik :
Mineral Tektosilikat (Q, K-Feld, Feldspatoid)
Fotomikroskopis nikol sejajar & silang